Deposition of thin films on a substrate surface is an important process in a variety of industries including semiconductor processing, diffusion barrier coatings and dielectrics for magnetic read/write heads. In the semiconductor industry, in particular, miniaturization requires atomic level control of thin film deposition to produce conformal coatings on high aspect structures. One method for deposition of thin films with control and conformal deposition is atomic layer deposition (ALD), which employs sequential, surface reactions to form layers of precise thickness. Most ALD processes are based on binary reaction sequences which deposit a binary compound film. Because the surface reactions are sequential, the two gas phase reactants are not in contact, and possible gas phase reactions that may form and deposit particles are limited.
ALD has been used to deposit metals and metal compounds on substrate surfaces. Al2O3 deposition is an example of a typical ALD process illustrating the sequential and self-limiting reactions characteristic of ALD. Al2O3 ALD conventionally uses trimethylaluminum (TMA, often referred to as reaction “A” or the “A” precursor) and H2O (often referred to as the “B” reaction or the “B” precursor). In step A of the binary reaction, hydroxyl surface species react with vapor phase TMA to produce surface-bound AlOAl(CH3)2 and CH4 in the gas phase. This reaction is self-limited by the number of reactive sites on the surface. In step B of the binary reaction, AlCH3 of the surface-bound compound reacts with vapor phase H2O to produce AlOH bound to the surface and CH4 in the gas phase. This reaction is self-limited by the finite number of available reactive sites on surface-bound AlOAl(CH3)2. Subsequent cycles of A and B, purging gas phase reaction products and unreacted vapor phase precursors between reactions and between reaction cycles, produces Al2O3 growth in an essentially linear fashion to obtain the desired film thickness.
In order to facilitate deposition, catalysts have been used during some ALD processes. Such catalysts have included amine-based catalysts. The catalyst is used to activate a reaction between two or more species. However, because the catalyst is aiding in the deposition process, the catalyst must be present near the surface of the substrate on which the film is intended to be grown; otherwise the reaction will not be catalyzed. Additionally, as the substrate temperature increases, the activity of the catalyst decreases. This makes the lifetime of the catalyst fairly low. To address these problems, one approach has been to increase the concentration of the catalyst in the deposition chamber, which should result in more catalyst at the surface. However, it is difficult to accomplish this while still keeping the vapor pressure sufficiently low enough to be practical in a deposition process. Thus, there is a need for improved methods of catalytic deposition.